Nice start. I would recomnend dumping the tie rod setup you have on there unless its a quarter miler only. Those open heim joint ends will eventually get dirt in them and grind up inside. Pick up some regular greasable inner and outer tie rods and adjuster sleeves if you plan on driving it a lot, and might possibly get caught in the rain. Car has the TVS system with tubular uppers. KYBs and front discs. Thats a great start. If you decide you want power discs and have a radical cam, you can go with a hydroboost setup and retain your power brakes.
I have an A833 o/d box but if you have the coin for a new box recommend the A588 as it is a bolt in. Whereas with the tremec your going to make a new trans tunnel, a modified trans mount, shorten the driveshaft, and hope the shifter comes out in the right spot if you decide to use a factory console.
A body 8.75 rear great axle if you got $1,200-$1,600 to burn on one, and still have rear drums.
Or an A body 8.25 mopar rear about $600 when done if you source gears and a sure grip from a junkyard grand cherokee 8.45.
Or use the search function on fabo for ford explorer 8.8 installs. It comes wit 3.5" axle tubes, heavy duty. At least as strong as an 8.75, lots of ratios available. Junkyard buy ins for the xploder sport trak (pickip xploder) at pick n pull range from $150 - $200 dont forget to take the explorer shock plates and U bolts, and an extra right side inner axle you need when cutting 3" off rhe longer left axle tube to shorten it to an A body width, and new weld on spring perches off evilbay for that bigger axle tube, and a ford/mopar bastard U joint
Sport trak axle has standard
Big bolt pattern
3.73 gears 3.90, 4.10 optional
Locking diff
Disc brakes